Ohm's Law confusion ...

[DeepCut]

Hi, something confusing me here.

I have a 12-volt, incandescent light bulb, the resistance of which is 17.5 Ohms.

According to Ohm's Law, if i allow the bulb 12 volts, the current flowing through it should be :

I = V/R = 12/17.5 = 0.7 Amps.

This sounded a lot to me for a tiny light bulb, so i powered it with my DC PSU (which has LCD readouts for Voltage/Current) and it only drew 75mA.

What is it that i don't know, does resistance go up when a load is powered ?


Any help greatly appreciated,

DC.

[DeepCut]

I think i've figured it, is it because of the rise in temperature in the filament ?


Cheers,

DC.

[Simon (Webmaster)]

Indeed, the resistance of the filament is a lot lower when cold than when heated up, hence why light bulbs tend to blow at switch-on.